Emblem.js is a ember friendly templating engine used as an alternative for handlebars.js.

Emblem.js doesn't have any official plugins for emacs. However they recommend to use slim plugins as they are similar.

slim-mode is available on melpa. To install it, run

M-x install-package slim-mode

After installing it, activate slim-mode by running M-x slim-mode.

Instead of activating manually, auto-mode-alist can be used to set major modes that needs to activated for files with specific extension. To activate slim-mode for emblem files which will be ending with .em or .emblem, use

(add-to-list'auto-mode-alist'("\\.\\(em\\|emblem\\)".slim-mode))

By adding this line to emacs configuration file, slim-mode gets activated for emblem.js files.